If else statement

i been trying to get the outcome of the grades to show a letter grade but its not working properly and i tried lots of way and still stuck.

for example, if i were to enter 90 for 5 grades and it comes to be an A and if i were to enter 5 grades of 80 it still comes out to be A. no matter how much i look at the program it seems good to me but if u guys could spot the mistake please let me know.